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Need help with baker's math in spreadsheet!

February 4, 2010 - 11:16pm

dmsnyder

Need help with baker's math in spreadsheet!

I am building a spreadsheet to help me develop formulas for breads. I'm gaining a much better understanding of baker's math in this process. However, I am getting some discrepancies in my calculations that I just can't seem to understand. I'm looking for help.

As an exercise, I'm working with a dough with the following parameters:

My spreadsheet calculates the amount of levain I need and how I should feed it. Another part of the spreadsheet calculates the amounts needed of each ingredient, including the levain. These two calculations of the levain amount are yielding different answers. I can't figure out why.

Can anyone explain why the Final Dough says I need 210.53 gms of levain, while the Levain calculations says I need 240 gms of levain?

It might assist someone help if you show the formula you are using in the spreadsheet cells.

My eye is drawn to hydration. Although you've indicated levain hydration at 50% in the desired parameters, in the lower calculation it appears to be 100% hydration.

I'm also unsure how the contribution of the water in the levain in the final dough contributes to the overall hydration in your calculations. If you seek a 78% hydration dough, and have a levain of a different hydration (is it 50%, is it 100%), do you need to be adding more/less water to make up for the fact the levain is not at 78%.....?

I'm not sure if I can help, but what I'm going to do is work through the calculations here to see if we can figure out where the discrepancies are.

Prefermented flour: 24% (133g)

Total Formula:

Flour -100% (555.5g)

Water -78% (433.5g)

Salt - 2% (11g)

Total: 180% (1000g)

Conversion factor: (1000g/180=) 5.55

Levain Build: (50% hydration)

Flour -100% (101g)

Water -50% (50.5g)

Starter -47% (47.5g=23.75g water +23.75g flour)

Total: 199g

Final Dough

Flour - 430.75g

Water - 359.25g

Salt - 11g

Levain - 199g

For starters there are differences in our final-dough amounts, but I haven't double-checked my calculations or compared them to your data, which was my objective. I have to run out the door now, but I'll check in later. I'm sure by that time you'll have received an answer from other, more knowledgeable Fresh Loafers.

Hey David, I've put both the baker's percentages and the ingredients weights in my caluclations. It's just that I calculated the exact amount of levain needed for your formula, i.e. no left over to feed. I suppose you have to decide whether or not you include the weight of the starter flour and water in the final dough.

My approach to calculating levains is to start with what I need. In your case, you need 210 grams of levain, which would be 48% of the final dough. Assuming you need to make some compensations for any levain sticking to the side of the bowl, let's say 215 grams to be safe.

According to your calculations, you want a 100% hydration, (100 grams each of flour and water) which, when added to the starter gives you 247 grams. 215/247 gives me a .87 conversion factor.

I have a formula designer spreadsheet that does exactly what you seem to be describing. It allows the design of 4 different loaves at a time (up to 4 different flours), combines the levain build, and creates a worksheet. Seriously handy

I'm not adverse to sending it to you and you can examine the formulas - if you want to message me an email address. No sense repeating the work. I don't have enough brain right now to thoroughly analyze your formulas...

I'm about to "go dark" prior to extended travel - but I will return your message when I can.

I'm not sure what formulas you've put in your spreadsheet, but here's my figures based on your input:

There are some things in your spreadsheet I don't understand. With a total dough yield of 180% and total dough weight 1000gr., the weight of prefermented flour should certainly be 133gr. Also, how come you mix the levain at 100% hydration when your input dictates 50%?

Where our calculations differ is in the ingredient weights for the Levain. Since the baker's %'s are the same, the difference must be in how we calculated the conversion factor. We agree on on total flour weight in the formula, and .24 x total flour weight is indeed 133.3 gms.

I don't get how to calculate the baker's %'s for the final dough. You got results like Yippee's. I'm missing something.

My calculation was incorrect. Can you share the formula you used to calculate the Conversion factor for the Levain? I'm stuck at the moment.

I'm just thinking out loud here. If any of this helps you, great; if not, just disregard it.

So, we know you need a total of 200g of levain for the final dough (133g flour + 67g water. Take what you need (200g) and divide it by the total number of flour and water units for the feeding (100 and 50, respectively): 200/150 = 1.33. We then take this result and multiply it by the above units to obtain the amount of flour and water need for the build. 1.33 x 100 = 133g flour; and 1.33 x 50 = 66.5g water. Now if you add this to the 47g (47%) starter you include in the levain build you'll end up 247g of levain, 47g of which you can use to perpuetuate your culture.

I follow Suas' formulas regarding baker's % for the final dough: Assume that the flour weight (not counting any "flour contributions" coming from the levain) of the final dough is 100%, and then calculate the remaining percentages based on that. Although it really is the total formula percentages that are the important ones, I feel it can be useful to sometimes list those for the final dough as well (especially when you're considering autolyse etc.).

To calculate the total weight of the levain build, I first calculate the weight of prefermented flour (133.3 gr.). Then I calculate the dough yield of the levain: Flour 100% + Water 50% + Starter 47% = 197%. So the total weight of the levain build should then be:

When I finally got my head on straight, I was able to understand how to calculate the needed percentages and quantities. It's interesting that I used a slightly different approach and ended up with the same result. My formulas for the Levain were:

As a matter of fact, we use the exact same way of calculating the levain, just different sets of numbers. The key is to figure out the connection between baker's percentages and weight: How many grams are contained in 1%?

We know the total flour weight in the levain and we know the total levain weight. So to figure out how many grams there are in 1%, either do what you did (133.3gr / 100% = 1.333 gr/ 1%) or what I sketched out (262.7gr / 197% = 1.333gr / 1%).

So, to figure out the weight of e.g. water, which is listed at 50%, you do: 50% * 1.333gr = 66.7gr.

By the way, it doesn't seem to me like you're a spreadsheet newbie: You even got colours and borders and stuff going on! Sophisticated! :)

I tried to figure where your math issues are but I did not find a specific location of your error. If you are an engineer you know (KISS) Keep It Simple Silly. I feel your conversion factor is messing up your calculations and I wonder if any of your formulas use either of the conversion factors as a factor. I would try again but this time only use simple math,+,-,*,/.

I bake just a little different so my spread sheets are looking for a different number in relation to things. I feed my starter twice a day and save all the discards in the fridge. I feed the first bit in the tub then just keep adding the discards to an and give it a nice stir. Within a few days I have a big amount of starter that has been working in the fridge for a number of days. My dough's use lots of pre-fermented starter in fact the pre-fermented flour is for the most part 50% of total flour. I find this also give me a nicer sourdough flavor. So my spreadsheets converts my total amount of starter into a bakers percentage and gives me a list of what and how much to add.

Nathan, I'm new to this bakers percentages but there is something about your calculations I don't understand. I don't know if it's my limited understanding so I will just ask.

If the Prefermented flour is 133g

In your Levan build you have flour @101g and flour in the starter @23.75g =124.75g is there a reason why this does not add up to 133g's or is my understanding of prefermented flour off?

I'm not the best at math, but my calculations will give you the exact amount of levain after the final build with nothing left over, which I normally don't do. I usually calculate so that I have about 20g left over after using the levain which I then feed and use to make more bread. Let's see if I can explain what I did clearly. The amount of levain that will be used in the dough is 199.5g which at 50% hydration is 133g flour + 66.5g water. The starter is 47% of 101g of flour.

I recalculated your formula based on my understanding that you are aiming for a final dough with 24% pre-fermented flour and 78% hydration. If my interpretation is incorrect, please let me know. My numbers are as follows for your reference:

The numbers in my Final Dough are just a different presentation of Hans' "Final Dough" percentages. He's expressing them in terms of 'Flour' while I was expressing them as the respective %s of ingredients in the final dough, as you will see below:

Using either approach (180% or 236.84%) will yield the same weight of ingredients. Hope this explains.

After reading and re-reading all your helpful comments and re-re-re-reading Hamelman, Suas and DeMuzio's sections on Baker's Math, I saw all my errors.

What I needed to do was:

1. Calculate the total baker's % and the ingredient weights for the Total Dough.

2. Calculate the ingredient amounts for the Levain and for the Final Dough using the Total Dough ingredient amounts. (The total baker's % for the Levain and Final Dough are not used in any calculations. Using them was my biggest error.)

3. Adjust the baker's % for water in the Final Dough (although that number is not used in any further calculations).

4. Substract out the initial Levain amount that is fed (the 47% of the Levain flour weight number) from the Levain used in the Final Dough.

If I do it this way, my numbers all come out to be exactly the same as hansjoakim's!

This whole exercise was a mind bender for me.

Faith - I'm not only not an engineer but I don't regard myself as much of a mathematician. I've also no prior spreadsheet experience beyond adding up columns of numbers.

Pat - Thanks for your offer, but it was important to me to "walk that lonesome highway by myself." Having to derive the formulas to do the calculations taught me more about baker's math and bread formula construction than any number of uses of an "off the shelf" spreadsheet or any number of re-readings of the best books could ever do.

This reminds me somewhat of my classical mechanics final exam in college physics. I'd studied formulas for lever and pulley problems, etc. for weeks. When I got the exam, I had a classic brain freeze. I couldn't remember any of them. After a half minute of panic, I reminded myself that all those special formulas were derived from Newton's laws. I knew and understood those. So, I derived the necessary formulas from basic principles, solved the exam problems and got 100% on the test. (The only one in my class to do so.) I value understanding more than knowledge. The latter is only a means to the former.

Thanks again to everyone who offered help. It really did the job to get me un-stuck.

David, Now that I know your not an engineer we can continue to talk....LOL I work with excell spread sheets all the time. In time you will find how much you can do with it. It's quite a powerfull tool. I made some sheets that use the pythagorean theorem for quick calculations. Sounds easy but try it some time.

the way I worked through it on my spreadsheet was to write out equations like:

Total wt of dough = total wt of flour + total weight of water

Total weight of water = weight of water in leavin build + weight of water in final mix

Wt of flour pre fermented = total wt of flour * % pre-fermented,

Total dough hydration = (Water in levain build + water in final mix) / (flour in levain build + flour in final mix)

etc

and then solved the simultaneous equations so that I could use total dough weight, overall hydration, mother starter hydration, levain build hydration, innoculation rate, and % flour prefermented as inputs.

Now there's an exercize best left to the reader.

I just didn't have enough brain to explain it all last Friday (and am not sure I have enough just today) and thought that seeing the actual formulas in a spreadsheet would be useful to you...

I was able to get my questions answered, although it seems there are always new questions.

I don't think there is a way to upload files (other than photos) to TFL. You can post a link to someplace else from which a file can be downloaded. At least, that's my understanding. I use DropBox for this.

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